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Mazza T, Roumeliotis TI, Garitta E, Drew D, Rashid ST, Indiveri C, Choudhary JS, Linton KJ, Beis K. Structural basis for the modulation of MRP2 activity by phosphorylation and drugs. Nat Commun 2024; 15:1983. [PMID: 38438394 PMCID: PMC10912322 DOI: 10.1038/s41467-024-46392-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Accepted: 02/26/2024] [Indexed: 03/06/2024] Open
Abstract
Multidrug resistance-associated protein 2 (MRP2/ABCC2) is a polyspecific efflux transporter of organic anions expressed in hepatocyte canalicular membranes. MRP2 dysfunction, in Dubin-Johnson syndrome or by off-target inhibition, for example by the uricosuric drug probenecid, elevates circulating bilirubin glucuronide and is a cause of jaundice. Here, we determine the cryo-EM structure of rat Mrp2 (rMrp2) in an autoinhibited state and in complex with probenecid. The autoinhibited state exhibits an unusual conformation for this class of transporter in which the regulatory domain is folded within the transmembrane domain cavity. In vitro phosphorylation, mass spectrometry and transport assays show that phosphorylation of the regulatory domain relieves this autoinhibition and enhances rMrp2 transport activity. The in vitro data is confirmed in human hepatocyte-like cells, in which inhibition of endogenous kinases also reduces human MRP2 transport activity. The drug-bound state reveals two probenecid binding sites that suggest a dynamic interplay with autoinhibition. Mapping of the Dubin-Johnson mutations onto the rodent structure indicates that many may interfere with the transition between conformational states.
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Affiliation(s)
- Tiziano Mazza
- Department of Life Sciences, Imperial College London, SW7 2AZ, London, UK
- Rutherford Appleton Laboratory, Research Complex at Harwell, Didcot, Oxfordshire, OX11 0FA, UK
- Department DiBEST (Biologia, Ecologia, Scienze Della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria, 87036, Arcavacata di Rende, Italy
| | - Theodoros I Roumeliotis
- Functional Proteomics group, Chester Beatty Laboratories, The Institute of Cancer Research, London, SW3 6JB, UK
| | - Elena Garitta
- Blizard Institute, Faculty of Medicine and Dentistry, Queen Mary University of London, E1 2A, London, UK
| | - David Drew
- Department of Biochemistry and Biophysics, Stockholm University, 10691, Stockholm, Sweden
| | - S Tamir Rashid
- Department of Metabolism, Digestion & Reproduction, Imperial College London, W12 0NN, London, UK
| | - Cesare Indiveri
- Department DiBEST (Biologia, Ecologia, Scienze Della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria, 87036, Arcavacata di Rende, Italy
- CNR Institute of Biomembranes, Bioenergetics and Molecular Biotechnology (IBIOM), 70126, Bari, Italy
| | - Jyoti S Choudhary
- Functional Proteomics group, Chester Beatty Laboratories, The Institute of Cancer Research, London, SW3 6JB, UK
| | - Kenneth J Linton
- Blizard Institute, Faculty of Medicine and Dentistry, Queen Mary University of London, E1 2A, London, UK
| | - Konstantinos Beis
- Department of Life Sciences, Imperial College London, SW7 2AZ, London, UK.
- Rutherford Appleton Laboratory, Research Complex at Harwell, Didcot, Oxfordshire, OX11 0FA, UK.
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Gutay-Tóth Z, Gellen G, Doan M, Eliason JF, Vincze J, Szente L, Fenyvesi F, Goda K, Vecsernyés M, Szabó G, Bacso Z. Cholesterol-Depletion-Induced Membrane Repair Carries a Raft Conformer of P-Glycoprotein to the Cell Surface, Indicating Enhanced Cholesterol Trafficking in MDR Cells, Which Makes Them Resistant to Cholesterol Modifications. Int J Mol Sci 2023; 24:12335. [PMID: 37569709 PMCID: PMC10419235 DOI: 10.3390/ijms241512335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2023] [Revised: 07/26/2023] [Accepted: 07/31/2023] [Indexed: 08/13/2023] Open
Abstract
The human P-glycoprotein (P-gp), a transporter responsible for multidrug resistance, is present in the plasma membrane's raft and non-raft domains. One specific conformation of P-gp that binds to the monoclonal antibody UIC2 is primarily associated with raft domains and displays heightened internalization in cells overexpressing P-gp, such as in NIH-3T3 MDR1 cells. Our primary objective was to investigate whether the trafficking of this particular P-gp conformer is dependent on cholesterol levels. Surprisingly, depleting cholesterol using cyclodextrin resulted in an unexpected increase in the proportion of raft-associated P-gp within the cell membrane, as determined by UIC2-reactive P-gp. This increase appears to be a compensatory response to cholesterol loss from the plasma membrane, whereby cholesterol-rich raft micro-domains are delivered to the cell surface through an augmented exocytosis process. Furthermore, this exocytotic event is found to be part of a complex trafficking mechanism involving lysosomal exocytosis, which contributes to membrane repair after cholesterol reduction induced by cyclodextrin treatment. Notably, cells overexpressing P-gp demonstrated higher total cellular cholesterol levels, an increased abundance of stable lysosomes, and more effective membrane repair following cholesterol modifications. These modifications encompassed exocytotic events that involved the transport of P-gp-carrying rafts. Importantly, the enhanced membrane repair capability resulted in a durable phenotype for MDR1 expressing cells, as evidenced by significantly improved viabilities of multidrug-resistant Pgp-overexpressing immortal NIH-3T3 MDR1 and MDCK-MDR1 cells compared to their parents when subjected to cholesterol alterations.
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Affiliation(s)
- Zsuzsanna Gutay-Tóth
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.G.-T.); (G.G.); (M.D.); (K.G.); (G.S.)
- Doctoral School of Molecular Cell and Immune Biology, University of Debrecen, 4032 Debrecen, Hungary
| | - Gabriella Gellen
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.G.-T.); (G.G.); (M.D.); (K.G.); (G.S.)
- Doctoral School of Molecular Cell and Immune Biology, University of Debrecen, 4032 Debrecen, Hungary
- MTA-ELTE Lendület Ion Mobility Mass Spectrometry Research Group, Department of Analytical Chemistry, Institute of Chemistry, ELTE Eötvös Loránd University, 1053 Budapest, Hungary
| | - Minh Doan
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.G.-T.); (G.G.); (M.D.); (K.G.); (G.S.)
| | - James F. Eliason
- Great Lakes Stem Cell Innovation Center, Detroit, MI 48202, USA;
| | - János Vincze
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary;
| | - Lajos Szente
- CycloLab Cyclodextrin Research & Development Laboratory, Ltd., 1097 Budapest, Hungary;
| | - Ferenc Fenyvesi
- Department of Pharmaceutical Technology, Faculty of Pharmacy, University of Debrecen, 4032 Debrecen, Hungary; (F.F.); (M.V.)
| | - Katalin Goda
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.G.-T.); (G.G.); (M.D.); (K.G.); (G.S.)
| | - Miklós Vecsernyés
- Department of Pharmaceutical Technology, Faculty of Pharmacy, University of Debrecen, 4032 Debrecen, Hungary; (F.F.); (M.V.)
| | - Gábor Szabó
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.G.-T.); (G.G.); (M.D.); (K.G.); (G.S.)
| | - Zsolt Bacso
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.G.-T.); (G.G.); (M.D.); (K.G.); (G.S.)
- Doctoral School of Molecular Cell and Immune Biology, University of Debrecen, 4032 Debrecen, Hungary
- Department of Pharmaceutical Technology, Faculty of Pharmacy, University of Debrecen, 4032 Debrecen, Hungary; (F.F.); (M.V.)
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Chai AB, Callaghan R, Gelissen IC. Regulation of P-Glycoprotein in the Brain. Int J Mol Sci 2022; 23:ijms232314667. [PMID: 36498995 PMCID: PMC9740459 DOI: 10.3390/ijms232314667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2022] [Revised: 11/18/2022] [Accepted: 11/22/2022] [Indexed: 11/27/2022] Open
Abstract
Maintenance of the tightly regulated homeostatic environment of the brain is facilitated by the blood-brain barrier (BBB). P-glycoprotein (P-gp), an ATP-binding cassette transporter, is expressed on the luminal surface of the endothelial cells in the BBB, and actively exports a wide variety of substrates to limit exposure of the vulnerable brain environment to waste buildup and neurotoxic compounds. Downregulation of P-gp expression and activity at the BBB have been reported with ageing and in neurodegenerative diseases. Upregulation of P-gp at the BBB contributes to poor therapeutic outcomes due to altered pharmacokinetics of CNS-acting drugs. The regulation of P-gp is highly complex, but unravelling the mechanisms involved may help the development of novel and nuanced strategies to modulate P-gp expression for therapeutic benefit. This review summarises the current understanding of P-gp regulation in the brain, encompassing the transcriptional, post-transcriptional and post-translational mechanisms that have been identified to affect P-gp expression and transport activity.
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Affiliation(s)
- Amanda B. Chai
- School of Pharmacy, Faculty of Medicine and Health, University of Sydney, Sydney, NSW 2006, Australia
| | - Richard Callaghan
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK
| | - Ingrid C. Gelissen
- School of Pharmacy, Faculty of Medicine and Health, University of Sydney, Sydney, NSW 2006, Australia
- Correspondence: ; Tel.: +61-2-8627-0357
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Budani M, Auray-Blais C, Lingwood C. ATP-binding cassette transporters mediate differential biosynthesis of glycosphingolipid species. J Lipid Res 2021; 62:100128. [PMID: 34597626 PMCID: PMC8569594 DOI: 10.1016/j.jlr.2021.100128] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 08/18/2021] [Accepted: 09/03/2021] [Indexed: 01/13/2023] Open
Abstract
The cytosolic-oriented glucosylceramide (GlcCer) synthase is enigmatic, requiring nascent GlcCer translocation to the luminal Golgi membrane to access glycosphingolipid (GSL) anabolic glycosyltransferases. The mechanism by which GlcCer is flipped remains unclear. To investigate the role of GlcCer-binding partners in this process, we previously made cleavable, biotinylated, photoreactive GlcCer analogs in which the reactive nitrene was closely apposed to the GlcCer head group, while maintaining a C16-acyl chain. GlcCer-binding protein specificity was validated for both photoprobes. Using one probe, XLB, here we identified ATP-binding cassette (ABC) transporters ABCA3, ABCB4, and ABCB10 as unfractionated microsomal GlcCer-binding proteins in DU-145 prostate tumor cells. siRNA knockdown (KD) of these transporters differentially blocked GSL synthesis assessed in toto and via metabolic labeling. KD of ABCA3 reduced acid/neutral GSL levels, but increased those of LacCer, while KD of ABCB4 preferentially reduced neutral GSL levels, and KD of ABCB10 reduced levels of both neutral and acidic GSLs. Depletion of ABCA12, implicated in GlcCer transport, preferentially decreased neutral GSL levels, while ABCB1 KD preferentially reduced gangliosides, but increased neutral GSL Gb3. These results imply that multiple ABC transporters may provide distinct but overlapping GlcCer and LacCer pools within the Golgi lumen for anabolism of different GSL series by metabolic channeling. Differential ABC family member usage may fine-tune GSL biosynthesis depending on cell/tissue type. We conclude that ABC transporters provide a new tool for the regulation of GSL biosynthesis and serve as potential targets to reduce selected GSL species/subsets in diseases in which GSLs are dysregulated.
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Affiliation(s)
- Monique Budani
- Division of Molecular Medicine, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada; Department of Laboratory Medicine & Pathobiology, University of Toronto, Toronto, Ontario, Canada
| | - Christiane Auray-Blais
- Division of Medical Genetics, Department of Pediatrics, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Québec, Canada
| | - Clifford Lingwood
- Division of Molecular Medicine, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada; Department of Laboratory Medicine & Pathobiology, University of Toronto, Toronto, Ontario, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada.
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Affiliation(s)
- Adam T. Clay
- Department of Molecular and
Cellular Biology and Biophysics Interdepartmental Group, University of Guelph, Guelph, ON, Canada N1G 2W1
| | - Peihua Lu
- Department of Molecular and
Cellular Biology and Biophysics Interdepartmental Group, University of Guelph, Guelph, ON, Canada N1G 2W1
| | - Frances J. Sharom
- Department of Molecular and
Cellular Biology and Biophysics Interdepartmental Group, University of Guelph, Guelph, ON, Canada N1G 2W1
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Abstract
This chapter deals with the interactions of two medically important multidrug ABC transporters (MDR-ABC), ABCB1 and ABCG2, with lipid molecules. Both ABCB1 and ABCG2 are capable of transporting a wide range of hydrophobic drugs and xenobiotics and are involved in cancer chemotherapy resistance. Therefore, the exploration of their mechanism of action has major therapeutic consequences. As discussed here in detail, both ABCB1 and ABCG2 are significantly affected by various lipid compounds especially those residing in their close proximity in the plasma membrane. ABCB1 is capable of transporting lipids and lipid derivatives, and thus may alter the general membrane composition by "flopping" membrane lipid constituents, while there is no such information regarding ABCG2. Still, both ABCB1 and ABCG2 show complex interactions with a variety of lipid molecules, and the transporters are significantly modulated by cholesterol and cholesterol derivatives at the posttranslational level. In this chapter, we explore the molecular details of the direct transporter-lipid interactions, the potential role of lipid-sensor domains within the proteins, as well as the application of experimental site-directed mutagenesis, detailed structural studies, and in silico modeling for examining these interactions. We also discuss the regulation of ABCB1 and ABCG2 expression at the transcriptional level, occurring through nuclear receptors involved in lipid sensing. The better understanding of lipid interactions with these medically important MDR-ABC transporters may significantly improve further drug development and clinical treatment options.
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Affiliation(s)
- Csilla Hegedüs
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary
| | - Ágnes Telbisz
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary
| | - Tamás Hegedűs
- MTA-SE Molecular Biophysics Research Group of the Hungarian Academy of Sciences, Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary
| | - Balázs Sarkadi
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary; MTA-SE Molecular Biophysics Research Group of the Hungarian Academy of Sciences, Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary
| | - Csilla Özvegy-Laczka
- MTA-SE Molecular Biophysics Research Group of the Hungarian Academy of Sciences, Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary.
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Guyot C, Hofstetter L, Stieger B. Differential effects of membrane cholesterol content on the transport activity of multidrug resistance-associated protein 2 (ABCC2) and of the bile salt export pump (ABCB11). Mol Pharmacol 2014; 85:909-20. [PMID: 24711118 DOI: 10.1124/mol.114.092262] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Rat canalicular membranes contain microdomains enriched in cholesterol and ATP-binding cassette transporters. Cholesterol is known to regulate the activity of transporters. Here, we investigated the effect of membrane cholesterol on the transport kinetics of multidrug resistance-associated protein 2 (MRP2) and of bile salt export pump (BSEP) variants and mutants. MRP2 and BSEP were expressed with baculoviruses in insect cells, followed by vesicle isolation from control and cholesterol-loaded cells (1 mM cholesterol@randomly methylated-β-cyclodextrin) for transport assays. We found that cholesterol stimulates MRP2 transport activity for substrates of different molecular weights: estradiol-17-β-glucuronide (E17βG), prostaglandin E2 (PGE2), cholecystokinin 8 (CCK8), and vasopressin displayed an increase of Vmax and a variable decrease of Km. Kinetics of E17βG showed a sigmoidal shape and a mild cooperativity in Hanes-Woolf plots in control membranes. High cholesterol content shifted E17βG to Michaelis-Menten kinetics. PGE2/glutathione transport followed Michaelis-Menten kinetics irrespective of cholesterol. The MRP2 substrates CCK8 and vasopressin exhibited Michaelis-Menten kinetics independent of membrane cholesterol content. Transport of ochratoxin A was ATP-dependent but was neither mediated by MRP2 nor stimulated by cholesterol. Transport of the two most common BSEP variants p.444V/A showed Michaelis-Menten kinetics irrespective of membrane cholesterol, whereby cholesterol leads to an increased Vmax while Km remains unchanged. The transport activity of the BSEP mutants p.E297G and p.R432T increased at high cholesterol content but did not reach the capacity of normal BSEP. Hence, changing membrane cholesterol content modulates BSEP and MRP2 transport kinetics differently. Cholesterol increases the transport rates of BSEP and MRP2, but with the latter, may also modify the binding site as for E17βG.
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Affiliation(s)
- Christelle Guyot
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, Zurich, Switzerland
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Telbisz Á, Hegedüs C, Váradi A, Sarkadi B, Özvegy-Laczka C. Regulation of the function of the human ABCG2 multidrug transporter by cholesterol and bile acids: effects of mutations in potential substrate and steroid binding sites. Drug Metab Dispos 2014; 42:575-85. [PMID: 24384916 DOI: 10.1124/dmd.113.055731] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
ABCG2 (ATP-binding cassette, subfamily G, member 2) is a plasma membrane glycoprotein that actively extrudes xenobiotics and endobiotics from the cells and causes multidrug resistance in cancer. In the liver, ABCG2 is expressed in the canalicular membrane of hepatocytes and excretes its substrates into the bile. ABCG2 is known to require high membrane cholesterol content for maximal activity, and by examining purified ABCG2 reconstituted in proteoliposomes we have recently shown that cholesterol is an essential activator, while bile acids significantly modify the activity of this protein. In the present work, by using isolated insect cell membrane preparations expressing human ABCG2 and its mutant variants, we have analyzed whether certain regions in this protein are involved in sterol recognition. We found that replacing ABCG2-R482 with large amino acids does not affect cholesterol dependence, but changes to small amino acids cause altered cholesterol sensitivity. When leucines in the potential steroid-binding element (SBE, aa 555-558) of ABCG2 were replaced by alanines, cholesterol dependence of ABCG2 activity was strongly reduced, although the L558A mutant variant when purified and reconstituted still required cholesterol for full activity. Regarding the effect of bile acids in isolated membranes, we found that these compounds decreased ABCG2-ATPase in the absence of drug substrates, which did not significantly affect substrate-stimulated ATPase activity. These ABCG2 mutant variants also altered bile acid sensitivity, although cholic acid and glycocholate were not transported by the protein. We suggest that the aforementioned two regions in ABCG2 are important for sterol sensing and may represent potential targets for pharmacologic modulation of ABCG2 function.
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Affiliation(s)
- Ágnes Telbisz
- Institute of Molecular Pharmacology, Research Centre for Natural Sciences, Hungarian Academy of Sciences (A.T., B.S.); Molecular Biophysics Research Group, Hungarian Academy of Sciences and Semmelweis University (C.H.); and Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences (A.V., C.O.-L.), Budapest, Hungary
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Bailly A, Yang H, Martinoia E, Geisler M, Murphy AS. Plant Lessons: Exploring ABCB Functionality Through Structural Modeling. Front Plant Sci 2011; 2:108. [PMID: 22639627 PMCID: PMC3355715 DOI: 10.3389/fpls.2011.00108] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2011] [Accepted: 12/17/2011] [Indexed: 05/18/2023]
Abstract
In contrast to mammalian ABCB1 proteins, narrow substrate specificity has been extensively documented for plant orthologs shown to catalyze the transport of the plant hormone, auxin. Using the crystal structures of the multidrug exporters Sav1866 and MmABCB1 as templates, we have developed structural models of plant ABCB proteins with a common architecture. Comparisons of these structures identified kingdom-specific candidate substrate-binding regions within the translocation chamber formed by the transmembrane domains of ABCBs from the model plant Arabidopsis. These results suggest an early evolutionary divergence of plant and mammalian ABCBs. Validation of these models becomes a priority for efforts to elucidate ABCB function and manipulate this class of transporters to enhance plant productivity and quality.
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Affiliation(s)
- Aurélien Bailly
- Plant Biology, Department of Biology, University of FribourgFribourg, Switzerland
- Institute of Plant Biology, Zurich–Basel Plant Science Center, University of ZurichZurich, Switzerland
| | - Haibing Yang
- Department of Horticulture and Landscape Architecture, Purdue UniversityWest Lafayette, IN, USA
| | - Enrico Martinoia
- Institute of Plant Biology, Zurich–Basel Plant Science Center, University of ZurichZurich, Switzerland
| | - Markus Geisler
- Plant Biology, Department of Biology, University of FribourgFribourg, Switzerland
- Institute of Plant Biology, Zurich–Basel Plant Science Center, University of ZurichZurich, Switzerland
- *Correspondence: Markus Geisler, Plant Biology, Department of Biology, University of Fribourg, Chemin du Musée 10, CH-1700 Fribourg, Switzerland. e-mail:
| | - Angus S. Murphy
- Department of Horticulture and Landscape Architecture, Purdue UniversityWest Lafayette, IN, USA
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Graham RM, Chua ACG, Carter KW, Delima RD, Johnstone D, Herbison CE, Firth MJ, O'Leary R, Milward EA, Olynyk JK, Trinder D. Hepatic iron loading in mice increases cholesterol biosynthesis. Hepatology 2010; 52:462-71. [PMID: 20683946 DOI: 10.1002/hep.23712] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
UNLABELLED Iron and cholesterol are both essential metabolites in mammalian systems, and too much or too little of either can have serious clinical consequences. In addition, both have been associated with steatosis and its progression, contributing, inter alia, to an increase in hepatic oxidative stress. The interaction between iron and cholesterol is unclear, with no consistent evidence emerging with respect to changes in plasma cholesterol on the basis of iron status. We sought to clarify the role of iron in lipid metabolism by studying the effects of iron status on hepatic cholesterol synthesis in mice with differing iron status. Transcripts of seven enzymes in the cholesterol biosynthesis pathway were significantly up-regulated with increasing hepatic iron (R(2) between 0.602 and 0.164), including those of the rate-limiting enzyme, 3-hydroxy-3-methylglutarate-coenzyme A reductase (Hmgcr; R(2) = 0.362, P < 0.002). Hepatic cholesterol content correlated positively with hepatic iron (R(2) = 0.255, P < 0.007). There was no significant relationship between plasma cholesterol and either hepatic cholesterol or iron (R(2) = 0.101 and 0.014, respectively). Hepatic iron did not correlate with a number of known regulators of cholesterol synthesis, including sterol-regulatory element binding factor 2 (Srebf2; R(2) = 0.015), suggesting that the increases seen in the cholesterol biosynthesis pathway are independent of Srebf2. Transcripts of genes involved in bile acid synthesis, transport, or regulation did not increase with increasing hepatic iron. CONCLUSION This study suggests that hepatic iron loading increases liver cholesterol synthesis and provides a new and potentially important additional mechanism by which iron could contribute to the development of fatty liver disease or lipotoxicity.
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Affiliation(s)
- Ross M Graham
- School of Medicine and Pharmacology, University of Western Australia, Perth, WA, Australia.
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Abstract
In humans, about 50 ABC proteins play physiologically important roles. Many ABC proteins are involved in lipid outward translocation and lipid homeostasis in the body, and defects in their functions cause various diseases. However, the precise mechanisms of substrate transport remain unclear. In bacteria, several ABC proteins are involved in the transport of lipoproteins and lipopolysaccharides from the inner to outer membrane, and their functioning is a prerequisite for survival. Their functions can be divided into "flip-flop" and "projection". In this review, human ABC proteins are compared to bacterial proteins to elucidate their mechanisms.
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Affiliation(s)
- Kohjiro Nagao
- Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University, Kyoto, Japan
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Abstract
MsbA is an essential ABC (ATP-binding cassette) transporter involved in lipid A transport across the cytoplasmic membrane of Gram-negative bacteria. The protein has also been linked to efflux of amphipathic drugs. Purified wild-type MsbA was labelled stoichiometrically with the fluorescent probe MIANS [2-(4′-maleimidylanilino)naphthalene-6-sulfonic acid] on C315, which is located within the intracellular domain connecting transmembrane helix 6 and the nucleotide-binding domain. MsbA–MIANS displayed high ATPase activity, and its folding and stability were unchanged. The initial rate of MsbA labelling by MIANS was reduced in the presence of amphipathic drugs, suggesting that binding of these compounds alters the protein conformation. The fluorescence of MsbA–MIANS was saturably quenched by nucleotides, lipid A and various drugs, and estimates of the Kd values for binding fell in the range of 0.35–10 μM. Lipid A and daunorubicin were able to bind to MsbA–MIANS simultaneously, implying that they occupy different binding sites. The effects of nucleotide and lipid A/daunorubicin binding were additive, and binding was not ordered. The Kd of MsbA for binding lipid A was substantially decreased when the daunorubicin binding site was occupied first, and prior binding of nucleotide also modulated lipid A binding affinity. These results indicate that MsbA contains two substrate-binding sites that communicate with both the nucleotide-binding domain and with each other. One is a high affinity binding site for the physiological substrate, lipid A, and the other site interacts with drugs with comparable affinity. Thus MsbA may function as both a lipid flippase and a multidrug transporter.
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Ito K, Hoekstra D, van Ijzendoorn SC. Cholesterol but not association with detergent resistant membranes is necessary for the transport function of MRP2/ABCC2. FEBS Lett 2008; 582:4153-7. [PMID: 19038257 DOI: 10.1016/j.febslet.2008.11.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2008] [Revised: 11/11/2008] [Accepted: 11/11/2008] [Indexed: 11/20/2022]
Abstract
MRP2(/ABCC2) excretes amphiphilic organic anions into bile, and associates with detergent-resistant bile canalicular membrane domains (DRM). Here, we have evaluated sensitivities of MRP2 transport function and DRM association by titrating the cellular cholesterol content. We demonstrate that the role of cholesterol in the partitioning of MRP2 to DRM can be separated from the role of cholesterol in the function of MRP2, such that (i) cholesterol is not necessary for the polarized distribution of MRP2 at the canalicular membrane, (ii) partitioning into DRM is not required for MRP2 function, yet (iii) the presence of cholesterol is necessary for transport activity.
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Ito K. ABCC2/Abcc2 Transport Property in Different Species and its Modulation by Heterogeneous Factors. Drug Metab Pharmacokinet 2008; 23:394-405. [DOI: 10.2133/dmpk.23.394] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Gao M, Yamazaki M, Loe DW, Westlake CJ, Grant CE, Cole SP, Deeley RG. Multidrug resistance protein. Identification of regions required for active transport of leukotriene C4. J Biol Chem 1998; 273:10733-10740. [PMID: 9553138 DOI: 10.1002/9781118705308.ch9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/27/2023] Open
Abstract
Multidrug resistance protein (MRP) is a broad specificity, primary active transporter of organic anion conjugates that confers a multidrug resistance phenotype when transfected into drug-sensitive cells. The protein was the first example of a subgroup of the ATP-binding cassette superfamily whose members have three membrane-spanning domains (MSDs) and two nucleotide binding domains. The role(s) of the third MSD of MRP and its related transporters is not known. To begin to address this question, we examined the ability of various MRP fragments, expressed individually and in combination, to transport the MRP substrate, leukotriene C4 (LTC4). We found that elimination of the entire NH2-terminal MSD or just the first putative transmembrane helix, or substitution of the MSD with the comparable region of the functionally and structurally related transporter, the canalicular multispecific organic anion transporter (cMOAT/MRP2), had little effect on protein accumulation in the membrane. However, all three modifications decreased LTC4 transport activity by at least 90%. Transport activity could be reconstituted by co-expression of the NH2-terminal MSD with a fragment corresponding to the remainder of the MRP molecule, but this required both the region encoding the transmembrane helices of the NH2-terminal MSD and the cytoplasmic region linking it to the next MSD. In contrast, a major part of the cytoplasmic region linking the NH2-proximal nucleotide binding domain of the protein to the COOH-proximal MSD was not required for active transport of LTC4.
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Affiliation(s)
- M Gao
- Cancer Research Laboratories, Queen's University, Kingston, Ontario K7L 3N6, Canada
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